the sound is only noticeable if you have an open exhaust system. there will be around a 5% mileage and hp gain but again, not that worth it unless you're a hardcore every last hp builder. oyea and if you have any sort of inspections...they frown on it...a lot.

if you really want one, just buy a bit of straight pipe and U bolt it in place if you can. or weld similar flanges to the end of a pipe and bolt it in. I've done both, both are easy and not all that worth it.

the sound is only noticeable if you have an open exhaust system. there will be around a 5% mileage and hp gain but again, not that worth it unless you're a hardcore every last hp builder. oyea and if you have any sort of inspections...they frown on it...a lot.

if you really want one, just buy a bit of straight pipe and U bolt it in place if you can. or weld similar flanges to the end of a pipe and bolt it in. I've done both, both are easy and not all that worth it.

yea but what would i do with the o2 sensor. i put a high flow hollow cat on my buddys 99 Si and it made the check engine come and say bad o2 sensor.

There may be a slight MPG gain but there certainly will not be a 5% HP gain. I liked the sound of no cat with a free flowing exhaust as well, but then I got tired of the gas smell and flaky O2 simulator so I had a Spintech 3" high flow cat put on...it had pretty much the same sound as without a cat. Some people do have issues with the SES and a high flow cat some don't, the best way is to have the post-cat O2 sensor related trouble codes disabled using a custom tune (like wait4me or pcmforless).

yea but what would i do with the o2 sensor. i put a high flow hollow cat on my buddys 99 Si and it made the check engine come and say bad o2 sensor.

You can tune it out, like Mint said, or you can buy an aftermarket cat with the 02 sensor bung already welded in (Maganaflow i know for sure has a few part numbers w/ the 02 included), or simply have the shop you go to weld an 02 sensor bung just behind the cat, and run the sensor there. In the event the sensor doesn't like the "high-flow" aftermarket piece, then you can allows block off the bung and go the de-tune route as previously mentioned.

yea, options for 2nd cat (I've never had to work on a car with a 2nd cat. repair or upgrade) but you can either reinforce, drill, and tap it or do an O2 simulator mod If you don't mind the test pipe legality you don't mind the o2 sim legality.

the mileage/power gain depends on the engine, exhaust system, and cat condition. I've seen cars gain more than 5%, I've seen cars have no measurable change.

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